GB2049057A

GB2049057A - Apparatus for controlling an hydraulic load

Info

Publication number: GB2049057A
Application number: GB8014616A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-05-12
Filing date: 1980-05-02
Publication date: 1980-12-17
Also published as: IT1131461B; FR2456866B1; FR2456866A1; DE2919206A1; US4429619A; JPS55154141A; GB2049057B; DE2919206C2; IT8021881A0

Description

1 GB 2 049 057 A 1

SPECIFICATION

Apparatus for controlling an hydraulic load 65 STATE OF THE ART The invention originates from an apparatus for controlling an hydraulic load according to the type set forth in the main claim. Such an apparatus for controlling an hydraulic load is already known from German AS 23 64 559 in which an injection cylinder of a plastics injection moulding machine is supplied with pressure medium from an electro-hydraulic servo valve.

With such apparatus for injection moulding machines, it is necessary, during the filling phase, for the servo motor to supply the injection cylinder with a very large quantity of pressure medium at low pressure drop across the valve whereas, in the suction phase, very small quantities of pressure medium need to be controlled. Moreover, the servo valve allows the pressure medium flowing to the injection cylinder to be controlled over a wider range with greater accuracy with regard to pressure and volume. The disadvantage with this apparatus is that the nominal through flow of the servo valve must be matched to the maximal quantity of.pressure medium-associated with the smallest permissible pressure drop across the valve. Thus, this apparatus is of expensive construction since it requires a large and expensive servo valve. In addition, with large servo valves, the accuracy of the pressure control with small through flow volumes reduces.

Furthermore, an apparatus for controlling an hydraulic load is known from U.S. specification

3 550 505 in which a throttle, the pressure difference of which acts on an auxiliary valve, is connected in a line leading from a pressure medium source to a multi-way valve. This throttle and auxiliary valve, together with further 100 constructional elements, and by means of a single pump in this apparatus serves for the control of two load circuits separated from one another entirely independently of one another.

Furthermore, with this apparatus, the multi-way 105 valve must be designed with its nominal through flow at the maximum volume of pressure medium flowing to the load.

ADVANTAGES OF THE INVENTION As opposed to this, the apparatus for controlling an hydraulic load in accordance with the invention comprising the characterising features of the main claim has the advantage that, with it, a greater volume of pressure medium can 115 be controlled in an analogue manner with respect to the nominal value of the servo valve which is used. Thus, in the small signal region, the accuracy and rapidity of the servo valve can also be fully utilized at a smaller nominal value. The 120 control elements required in addition to the servo valve are considerably less costly than the difference in price between a large and a small servo valve.

Advantageous further developments and improvements of the apparatus set forth in the main claim are possible due to the measures set forth in the sub-claims. An especially advantageous arrangement is produced in accordance with claim 3 whereby, with hydraulic loads, this apparatus may achieve a high extension speed together with a low retraction speed.

Furthermore, an arrangement according to claim 5 of special preference because in this manner the hydraulic load can achieve a rapid traverse speed in both directions. Further particular advantageous arrangements will become apparent from the other sub-claims, the description and the drawing.

DRAWING Three embodiments of the invention are illustrated in the drawing and are described in detail in the following specification. Figure 1 shows a first apparatus for controlling an hydraulic load in simplified representation, Figure 2 shows another type of construction of the auxiliary valve in the apparatus according to Figure 1 and Figures 3 and 4 show a second and third apparatus respectively in simplified representation.

DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows an apparatus 10 which has as esential components, an electro-hydraulic servo valve 11, an auxiliary va_lve 12 associated go therewith and a double-acting cylinder 13. A supply port 14 to the servo valve 11 is in communication through a first line section 15 with the output from a pump 16 which withdraws pressure medium from a reservoir 17. A return line 19 to the reservoir 17 leads from the return port 18 of the servo valve 11. A first load port 21 of the servo valve 11 is in communication through a second line section 22 with a first port 23 of the cylinder 13. Moreover, the first port 23 is associated with the larger effective area of the piston 24 in the cylinder 13. The first line section 15 and the second line section 22 form a line 25 leading from the pump 16 to the cylinder 13. A third line section 27 leads from a second load port 26 to a second port 28 of the cylinder 13. A measuring throttle 29 is connected in the first line section 15. Upstream of the measuring throttle 29, a first control line 31 branches from the first line section 15 and leads to an input 32 to the auxiliary valve 12. Furthermore, downstream of the measuring throttle 29, a second control line 33 branches from the first line section 15 and leads to a control port 34 of the auxiliary valve 12. An auxiliary line 36 leads from an output 35 from the auxiliary valve 12 to the second line section 22. The auxiliary valve 12 has a slide valve member 37 the first end 38 of which is loaded by the force of the spring 39 as well as the pressure in the control port 34. The pressure upstream of the measuring throttle 29 acts on the opposite, equally large, second end 41 of the slide valve member 37. The slide valve member 37 is retained by the spring 39 in an illustrated initial position in which it blocks the communication from the input 32 to the output 35. The slide valve member 37 is displaceable by a pressure 2 GB 2 049 057 A 2 difference occuring at the measuring. throttle 29 and against the force of the spring 39 into working positions in which the slide valve member 37 controls a volume of pressure medium from the input 32 proportional to the pressure difference acting on it with the aid of the openings 42.

The method of operation of the apparatus 10 is as follows: if the control valve member of the servo valve 11 is located in the illustrated central position and the slide valve member 37 of the auxiliary valve 12 is located in the illustrated initial position, then the piston 24 is hydraulically locked in the cylinder 13. If the control slide of the servo valve 11 is then displaced towards the left - with reference to Figure 1 and the input port 14 is thereby connected to the first load port 2 1, then pressure medium flows from the pump 16 through the line 22 to the first port 23 at the cylinder 13.

This pressure medium flowing to the cylinder 13 generates a pressure difference across the 85 measuring throttle 29 which acts on the slide valve member 37 in the auxiliary valve 12 through the control lines 31, 33. If this pressure difference at the measuring throttle 29 exceeds a value predetermined by the pre-tensioning of the spring 39 and the overlapping of the slide valve member 37, then the auiliary valve member 37 opens and permits a volume proportional to the pressure difference to flow from the input 32 to the output 37. Thus, parallel to the quantity of pressure medium flowing through the servo valve 11 to the port 23 of the cylinder 13, a further pressure medium flow flows from the pump 16 through the first control line 3 1, the auxiliary valve 12 and the auxiliary line 36 to the port 23 at the cylinder 13. Thus, by means of the servo valve 11, a quantity of pressure medium can be controlled to the cylinder 13 in an analogue manner with respect to the electrical input signal and which is substantially greater than the nominal through flow associated with the servo valve 11. On the other hand, if only small quantities of pressure medium are controlled to the port 23 of the cylinder 13 then the communication through the 45' auxiliary valve 12 is blocked by the slide valve member 37.and the entire quantity of pressure medium flows through the line 22; in so doing, the high accuracy of the servo valve 11 can be fully utilized. The flow volume occurring in the rod side of the cylinder 13 is so small due to the area ratio 115 that it can be returned through the servo valve 11 without any auxiliary device.

If the control slide of the servo valve 11 is displaced in the reverse manner towards the right and thereby the piston 24 together with the piston rod is retracted, then pressure medium flows from the pump 16 through the first line section 15, the servo valve 11 and the third line section 27 to the port 28 at the cylinder 13. The oil flowing away from the cylinder 13 flows from the first port 23 through the second line section 22, the servo valve 11 and the return line 19 to the reservoir 17. The servo valve 11 and the measuring throttle 29 are so matched to one another that during retration of the piston rod on the piston 24 the pressure difference occurring across the measuring throttle 29 cannot open the slide valve member 37 of the auxiliary valve 12. This assumes a relatively low retraction speed of the piston 24 which is usual for injection cylinders of plastics injection moulding machines.

Figure 2 shows a second auxiliary valve 45 which, instead of the auxiliary valve 12 in Figure 1, is switchable in the control lines 31, 33 or the auxiliary line 36. The auxiliary valve 45 differs from that according to Figure 1 chiefly by another slide valve member 46 and by a second control port 47 separated from the input 32. Moreover, like parts in Figure 1 are provided with like references. By means of the auxiliary valve 45, a separation between the controlled flow volume and the controlling pressure may be achieved.

Figure 3 shows a second apparatus 50 which differs from the apparatus 10 according to Figure 1 as follows, wherein like parts are provided with like references. In the apparatus 50 the measuring throttle 29 is connected in the second line section 22. Furthermore, the apparatus 50 has an auxiliary valve 51 which has three ports 52, 53 and 54 as well as two control ports 55, 56. From the first port 52, an auxiliary line 57 leads to the second line section 22 in the region between the measuring throttle 29 and the first port 23 at the cylinder 13. The second port 53 of the auxiliary valve 51 has communication with the return line 19 through a line 58. From the third port 54, a line 59 leads to the first line section 15 and thus to the output from the pump 16. From the first port 52 on the auxiliary valve 51, a first control line 61 leads through a damping throttle 62 to the first control port 55. A second control line 63 branches from the second line section 22 in the region between the servo valve 11 and the measuring throttle 29 and leads to the second control port 56. The auxiliary valve 51 has a slide valve member 64 which is centred by two springs 65, 66 into its central position in which it blocks the communications between the ports 52, 53, 54.

The method of operation of the apparatus 50 is as follows: if the control slide of the servo valve 11 and of the auxiliary valve 51 are in their illustrated central positions then the piston 24 is hydraulically locked in the cylinder 13. If the control slide of the servo valve 11 is moved towards the right - with reference to Figure 3 then the pump 16 delivers pressure medium through the line 25 to the first port 23 of the cylinder. The pressure medium flowing to the port 23 at the cylinder generates a pressure difference across the measuring throttle 29 which acts on the ends of the slide valve member 64 through the control lines 61, 63 and the auxiliary line 57. Moreover, if the servo valve 11 is moved to such an extent that the pressure difference at the measuring throttle 29 exceeds a predetermined value then this pressure differenc forces the slide valve member 64 of the auxiliary valve 51 towards the left, with reference to Figure 3, against the force of the spring 65. Thus, the slide valve member 64 controls a communication from the C 3 GB 2 049 057 A 3 third port 54 to the first port 52. Pressure medium flowing parallel to a further flow then flows from the pump 16 through the line 59, the auxiliary valve 5 1 and the auxiliary line 57 to the port 23 at the cylinder, parallel to the pressure medium flowing from the pump 16 through the line 25 and the servo valve 11 to the port 23 at the cylinder 13. The quantity of the pressure medium flowing through the auxiliary valve 51 is therefore proportional to the value of the pressure difference at 29. Thus, by means of the servo valve 11, a flow of pressure medium can be cotnrolled to the port 23 at the cylinder 13 the value of which behaves in an analogue manner with respect to the electrical input signal at the servo valve 11.

Moreover, this flow can be subtantially greater than the maximal through flow determined by the nominal value of the servo valve 11. Furthermore, when the servo valve 11 controls only small pressure medium flows and the slide valve 85 member 64 of the auxiliary valve 51 takes up its central locking position, the accuracy of the servo valve 11 can be fully utilized.

If, for retracting the piston rod on the piston 24, the control slide of the servo valve 11 is displaced 90 towards the right - with reference to Figure 3 - then the pump 16 delivers pressure medium through the first line section 15, the servo valve 11 and the third line section 27 to the second port 28 at the cylinder 13. Oil flowing through the first port 23 from the cylinder 13 flows through the second line section 22 and the servo valve 11 and the return line 19 to the reservoir 17. In so doing, if the pressure difference existing at the measuring throttle 29 lies below a predetern-iined pressure difference effecting response of the auxiliary valve 51, then the slide valve member 64 remains in its central position and blocks the first port 52. On the other hand, if the pressure drop occurring at the measuring throttle 29 exceeds the predetermined pressure difference, then it forces the slide valve mernber 64 in the auxiliary valve 51 towards the right against the force of the spring 66. In so doing, the slide valve member 64 opens a communication from the first port 52 to the second port 53. Thus, in addition to the pressure medium flowing from the cylinder 13 110 through the servo valve into the reservoir, a further stream can flow parallel thereto through the auxiliary line 57, the auxiliary valve 51 and the line 58 likewise to the reservoir 17. Thus, as distinct from the apparatus according to Figure 1, the high 115 speed of the piston can not only be achieved during extension of the piston rod but also during retraction of the piston rod by means of the apparatus 50.

Figure 4 shows a third apparatus 70 which differs from the apparatus 50 according to Figure 3 as follows, wherein like parts are provided with like references. Primarily, the apparatus 70 has a cylinder 71 with equally large effective areas as well as another auxiliary valve 72 which, in addition to its two control ports 55, 56, has five ports 73 to 77. Amongst the latter there is a central supply port 75, to both sides thereof a first (74) and a second load port 76 as well as the outermost first port 73 and the second return port 77. The supply port 75 and the return ports 73, 77 are connected in an appropriate manner to the lines 59 and 58. Moreover, the second load port of the auxiliary valve 72 is connected in a similar manner to the auxiliary line 57. A second auxiliary line 78 leads from the first load port 74 to the third line section 27.

The method of operation of the apparatus 70 corresponds completely to that of the' apparatus according to Figure 3; with it a rapid extension and retraction of the piston rod in the cylinder 77 may also be achieved, in this instance the cylinder having equally effective areas and also acting as an equal stroke cylinder.

Variations in the illustrated embodiments are of course possible without departing from the concept of the invention. Thus, the illustrated apparatus is not restricted to the use of doubleacting cylinders. The apparatuses can also be used with advantage for controlling single-acting loads or hydraulic motors. Not only the usual electrohydrolic servo valves of single or multi-stage construction can be used but also the usual proportional values can be used for the illustrated servo valve. Also the construction of the auxiliary valves can be modified without departing from the concept of the invention.

Claims

1. Apparatus for controlling an hydraulic load comprising at least one line leading from a pressure medium source to the load and in which is Connected an electro-hydraulically actuated control valve, characterised in that a measuring throttle is connected in the line in series with the control valve and its pressure difference controls a spring loaded slide valve member of an auxiliary valve which is connected in a pressure medium connection which branches from the line in the region between the pressure medium source and the control valve and leads to the line in the region between the control valve and the load and that the control valve and the measuring throttle are in parallel with the said pressure medium connection.

2. A pparatus according to claim 1 characterised in that the electro-hydraulically actuated control valve is a servo valve.

3. Apparatus according to claim 1 characterised in that the control valve is a proportional valve provided with a proportional magnet actuating its control slide directly or indirectly. 120

4. Apparatus according to one of claims 1 to 3 characterised in that the measuring throttle is connected in a line upstream of the control valve and the control lines branch from the first line section to the auxiliary valve upstream and downstream of the measuring throttle.

5. Apparatus according to claim 4 characterised in that the auxiliary valve is formed as a 2-way valve the slide valve member of which, 4.

GB 2 049 057 A 4 loaded by a spring, takes up an initial position blocking the pressure medium connection and opens the said communication in proportion to the pressure difference across the measuring throttle.

6. Apparatus according to one of claims 1 to 3 characterised in that the measuring throttle is connected in a second line section downstream of the control valve and from the said portion of the line two control lines branch to the auxiliary valve upstream and downstream of the measuring 35 throttle.

7. Apparatus according to claim 6 characterised in that the auxiliary valve is formed as a 3-way valve the slide valve member of which when in a spring centred central position, separates three ports from each other and on displacement out of the said position in both directions connects a first port connected to the load alternately with a second port connected to a return or to a third port connected to the pressure medium source.

8. Apparatus according to one of claims 1 to 7 characterised in that the load has two ports and a differential piston and that the port associated with the larger piston area is in communication with the auxiliary valve.

9. Apparatus according to one of claims 1 to 8 characterised in that the control valve the auxiliary valve and the measuring throttle are arranged in one housing.

10. Apparatus according to one of claims 1 to 9 characterised in that the cylinder is the injection cylinder of a plastics injection moulding machine.

11. Apparatus according to claim 6 characterised in that the auxiliary valve is formed as a 5-way valve the slide valve member of which when in a spring centred central position separates five ports from one another and on displacement out of the said position in both directions connectes one of the load ports to the supply port and the other load port to the return Oort and that a second auxiliary line leads from the first load port to the third line section.

12. Apparatus according to claim 11 characterised in that the cylinder is double-acting and has effective areas of equal size.

13. Apparatus for controlling an hydraulic load substantially as herein described with reference to Figure 1, Figure 2, Figure 3 or Figure 4 of the accompanying drawings.

Printed for Her Majestys Stationery Office by the Courier Press. Leamington Spa, 1980. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies maybe obtained.

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